In general, welding using high energy density beams such as laser beam is widely applied especially where fine welding or neat appearances are required, because an instantaneous melting is possible through the use of high energy beam so that the welding can be performed very quickly and the penetration is deepened and thernal distortions of the target object are reduced by means of a very narrow beam so that a high welding quality can be achieved.
Gap constraint required for a conventional butt welding using high energy density beam is as follows:g≦min(0.1t,0.15d˜0.3d)
where t (mm) is the thickness of a plate as the target object, g (mm) is the gap in a joint on the target object, d (mm) is the focus diameter of the high energy density beam, b (mm) is the width of a weld, and h (mm) is the height of a weld, and, in case the plate is made of steel or aluminum having a thickness of 1˜3 mm, the good weld width is in the range of:b=1˜4 mm.
Therefore, the conventional butt welding using high energy density beam can be applied to very limited cases, and a welding wire is employed for performing the high energy density beam welding in a wide range of cases where the gap g does not meet the above constraints.
FIG. 1 shows a schematic diagram depicting a conventional high energy density beam welding system using a welding wire.
A weld is formed by melting simultaneously a front end of a welding wire 6 and a portion to be welded on a target object 9 by means of a high energy density beam 3 emitted from a beam generator 1 through a focus regulator 2. Therefore, it is required that the focus of the high energy density beam 3 be located at the front end of the welding wire 6 provided by a wire supplier 4 and the portion to be welded on the target object 9 with a discrepancy of 1 mm or less.
Meanwhile, shielding gas purges onto the portion to be welded on the target object 9 from a shielding gas nozzle 8 connected to a shielding gas supplier 7 to prevent the portion to be welded from oxidation and impurities.
Reference numeral 5 designates a wire guide for guiding the welding wire 6 provided by the wire supplier 4 such that it can be accurately delivered to the portion to be welded.
Because an error in the feeding position must be minimized, the welding wire supplier needs to be more complicated by reducing the vibration of the front end of the welding wire 6 and maintaining a contacted position to be touched. In addition, since the high energy density beam 3 melts not only the target object 9 but also the welding wire 6, an energy loss in the high energy density beam is so high to significantly lower the process speed and the efficiency of the welding.
To solve the latter problem, there have been developed such methods as to preheat the welding wire 6 and put it into a melting pool. However, these methods require an additional device which needs to be integrated to the welding wire supplier, which is not efficient and constrained in the operations.
Besides, since the high energy density beam 3 melts not only the target object 9 but also the welding wire 6, a heat input in the portion to be welded is so great that the portion to be welded is subject to significant thermal distortion, finally deteriorating the overall welding quality.
In case the gap g is too wide to be within the constraints for high energy density beam welding, it is possible to perform an arc and high energy density beam hybrid welding.
However, this method has drawbacks in that a heat input in the portion to be welded is within the same order but the width of the molten portion is almost as twice as the case of the high energy density beam welding, and in addition, the thermal distortion is more severe compared thereto.
Moreover, arc and charring occurs between the welding wire and the target object and a stable condition is dependent on the characteristics of the material and the environment, such as the distance, angle and direction between the arc welder and the target metal.
In conclusion, although the hybrid welding may be applied to the case where the gap is wide, it is not suitable for providing a high welding quality, for example, in the case where a neat appearance is required.